This application is a national phase of PCT/FR00/01506 which was filed on May 31, 2000, and was not published in English.
The present invention relates to a chip comprising a plurality of electrodes and a method for populating such a chip.
Within the scope of the invention, and by analogy with the meaning of the word in the field of micro-electronics, xe2x80x9cchipxe2x80x9d refers to a small solid part with at least one main surface and one, or more functional parts or components. The typical measurements of a chip can be for example 1 cmxc3x971 cmxc3x970.1 cm.
In the present invention, the components of the chip are studs or electrodes that are functionalized and disposed, for example, in a regular orthogonal network.
The invention has applications in the field of biological or chemical sensors. The electrodes are then functionalized individually, being coated with a reagent capable of reacting with a given chemical molecule or capable of fixing a given biological material such as a strand of DNA.
The various electrodes of a single chip can be coated with various reagents capable of reacting with various molecules or various types of DNA strands. The molecules or biological material are then referred to as chemical or biological xe2x80x9ctargetsxe2x80x9d.
Chips, the electrodes of which are coated with various biological sensors, i.e. with reagents sensitive to certain biological targets, are referred to as DNA chips.
The invention also has applications in producing identification or calibration parts for which the electrodes are selectively coated with stable metal isotopes such as iron, nickel or cobalt.
Among the various techniques generally implemented to coat the electrodes of chips or DNA chips, techniques are particularly used that use electronic addressing of the electrodes. Electronic addressing is used to cause a coating deposit to form selectively on the addressed electrodes.
To this end the chip is successively brought into contact with one or more mediums, particularly electrolytes, and the formation of the coating deposit is initiated by applying a polarization voltage to the selected electrodes.
Alternatively, the coating deposit can also be formed as a result of an electrolytic current that is passed through the medium from the selected electrodes to one or more counter-electrodes.
In order to simplify the description the voltages applied to the electrodes or the electrolytic currents initiated from the electrodes are referred to below as xe2x80x9cpolarizationxe2x80x9d voltage and current.
An illustration of the techniques mentioned above is given in French patent FR-A-2 754 276 or in French patent FR-A-2 741 476 that concerns a method for collectively producing chips selectively coated with a deposit.
The electrodes are generally electrically addressed via a plurality of addressing terminals provided, for example, on one edge of the chip and electrically connected to the electrodes by connection lines embedded in the base of the chip.
When there are a small number of electrodes on the surface of the chip each addressing terminal can be individually connected to an electrode.
However, when there are a large number of electrodes a complex connection network and a system for multiplexing the electrical addressing commands is required for the selective and individual polarization of each electrode.
The complexity of the addressing system considerably increases the cost of the chips and multiplies the rate of faulty chips due to defective internal connections. It is therefore necessary to perform a test ensuring correct operation at various stages in the chip production process to eliminate defective chips at every stage.
This has an impact on the yield of the chip production process and the cost.
The aim of the present invention is to propose an improved chip enabling electrodes to be coated selectively while avoiding the drawbacks mentioned above.
A particular aim is to apply polarization voltages or currents to the electrodes without resorting to a complex electronic addressing network and multiplexing systems.
A further aim is to propose a chip that can comprise a very large number of electrodes and yet be reliable and economic to produce.
A final aim is to propose a method for coating such a chip that is simple to implement.
More precisely, to achieve these aims the invention relates to a chip comprising:
a base,
electrodes provided on a surface of the base and
a plurality of electric generators integrated in the base and connected to a plurality of said electrodes such that each electrode is only connected to a single generator.
The electrodes can be advantageously separated from each other such that they constitute either microgrooves or projecting structures known as xe2x80x9cmesasxe2x80x9d.
xe2x80x9cElectric generatorsxe2x80x9d refer to components capable of providing a voltage or electric current in response to external, particularly thermal, luminous or mechanical stimulus applied to the chip.
In particular, the generators used to produce the chip of the invention can be thermoelectric, photo-voltaic or piezo-electric generators.
Each generator is preferably located in the base near one or more electrodes to which it is connected.
In one particular embodiment of the chip the base of the chip may comprise a transparent substrate to activate the electric generators by means of at least one beam of light.
The base material of the substrate is selected to be transparent particularly to the wavelength or range of wavelengths of an insolation beam used to selectively light or heat one or more electric generators.
When they are photo-voltaic-type generators each one can comprise at least one junction of semi-conductors with a first region of a first type of conductivity connected to at least one electrode and a second region of a second type of conductivity connected to a counter-electrode.
The two regions together constitute the junction. They can be created by doping a layer of single- or poly-crystal silicon.
These generators, which are photo-voltaic cells, can also be produced using other materials such as hydrogenated amorphous silicon, gallium arsenide, germanium, silicon carbide or indium phosphide for example. The choice of semi-conductor material determines the height of the forbidden band and thus enables the nominal voltage of the generator to be set. It also sets the optical absorption properties and therefore the excitation wavelength range of the generators. Table I below gives the values of the forbidden band (Gap) of the zero-current voltage (Vco) and the short-circuit current (Isc) authorized by the main materials which are used alone or combined to produce the generators. xe2x80x9cCombined usexe2x80x9d is understood to mean connecting two photo-voltaic junctions such as GaInP/GaAs in series.
One or more counter-electrodes can be provided to pass an electrolytic current through a medium containing the deposit material. They can be created on the same base or separated from the base but electrically connected to the electric generators.
The chips of the invention can be independent or associated in a system of a plurality of adjacent chips which are created, for example, on the same wafer of semi-conductor material.
The invention also relates to a method for coating a chip such as that described above comprising one or more generators. According to the method the electrodes are brought into contact with a medium capable of creating a deposit when a voltage and/or polarization current is applied and at least one electrical generator is selectively activated to cause selective polarization of at least one electrode connected to said generator. The generators are activated by means that are external to chip, for example a beam of light or a beam of electrons.
When the generator is a light-sensitive photo-voltaic generator a visible or UV beam of light is preferably selected whereas when the generator is thermoelectric a visible, UV or infrared beam of light may be selected.
According to one particular implementation of the method, the beam of light can be applied by means of a light-source comprising a plurality of individual light-sources arranged such that it matches respectively said plurality of electric generators of the chip. The medium capable of creating a deposit can be a fluid medium, particularly liquid, or possibly a powder.
In this particular implementation the electrodes of the chip are preferably arranged according to an orthogonal network that is more or less regular and that matches a strip or array of electroluminescent diodes or laser diodes used as individual sources. The individual sources can be mounted in a base which may be equipped with a network of microlenses adjusted to the sources and on which a chip or assembly of chips can be deposited for the luminous addressing of the generators.
In one variant the beam of light can also be applied from a source of scattered light using an insolation mask. The mask has apertures that selectively match the electric generators to be activated.
This type of insolation technique is particularly simple to implement as it uses techniques known in the field of photolithography to produce electronic chips.